The present invention relates to a droplet deposition apparatus such as, for example, a drop-on-demand inkjet printer.
A typical drop-on-demand ink jet printer includes one or more printheads mounted on the carriage or printer body of a printer, with ink being ejected from one or more ink reservoirs located in the printer through nozzles formed in the or each printhead.
In view of the demand for higher resolution drop-on-demand inkjet printing, it is desirable to control accurately the precise locations at which ink ejected from the nozzles lands on a print surface. Accordingly, each printhead is individually aligned on the carriage or printer body. If one of the printheads were to become defective in any way, it is necessary to remove the defective printhead and re-align accurately the replacement printhead on the carriage or printer body. This can be a difficult, and therefore time-consuming, operation.
In its preferred embodiments, the present invention seeks to solve these and other problems.
In a first aspect, the present invention provides droplet deposition apparatus comprising a base and a printhead adjustably mounted on the base and positionable relative to a datum on the base such that a swath of print produced by the printhead is in a predetermined position relative to the datum, the base being locatable on a printer using the datum.
As the swath of print produced by a printhead is aligned with a datum formed on the base and used to mount the base to the printer, the printhead can be easily replaced without any loss of alignment of the produced print swath relative to the carriage or body of the printer. The alignment of the swath with a single datum formed on the base also improves the ease of alignment of the swath relative to the carriage or printer body; as the print may be ejected at an angle to the axes of the nozzles of the printhead, the position of the printhead is adjusted in relation to the produced print swath.
In a preferred arrangement, the apparatus comprises a plurality of printheads, each printhead being adjustably mounted on the base and positionable relative to the datum on the base such that swathes of print produced by the printheads are in respective predetermined positions relative to the datum.
Thus, the above advantages in respect of a single printhead are also provided with a multi-printhead arrangement, so that, for example, if the printer were to become defective, the base can be removed from the defective printer and accurately mounted on the replacement printer using the datum, that is, without having to re-align each individual printhead, so that the swaths of print to be produced by the printheads are still in the correct alignment.
Furthermore, when using a plurality of printheads in order to increase print width, it is important that the first nozzle of a second printhead is positioned as close as possible to one pitch after the last nozzle of the first printhead in order to maintain a high print quality between the printheads. By means of the present invention, this positioning can be conducted quickly and easily.
The printheads may be arranged in pairs on the base, for example, side-by-side pairs. This can increase the density of the mounting of the printheads on the base, thus providing for a compact droplet deposition apparatus.
In a preferred embodiment, the apparatus comprises means for adjusting the position of the or each printhead on the base relative to the datum. This can enable individual printheads to be positioned on the base so that the swaths of print produced by the printheads are in the predetermined positions relative to the datum.
The adjusting means may comprise means for adjusting the location of the or each printhead relative to the datum and means for adjusting the orientation of the or each printhead relative to the datum. Thus, the location and orientation of the printhead on the base can be individually adjusted.
The adjusting means may comprise a plurality of adjustment members engaging the or each printhead, each adjustment member being movable relative to the base so as to adjust the position of the printhead on the base. For example, each adjustment member may comprise a tapered surface, the printhead being urged against the tapered surface so that movement of a tapered surface relative to the base adjusts the position of the printhead on the base. One suitable adjustment member is a tapered screw having a screw thread engaging a conformingly-profiled threaded bore formed in the base, with axial movement of the screw within the bore causing the printhead, urged against the tapered surface, to move relative to the base. As the motion of the screw within the bore may be accurately controlled, the alignment of the swath of print from the printhead with the datum on the base is thus also accurately controlled.
The printhead may have a conformingly tapered surface engaging the tapered surface of the adjustment member. The engagement of the conformingly tapered surfaces can enable the printhead to be held against the base by the adjustment members.
The apparatus preferably comprises means, resiliently mounted on the base, for urging a printhead against the adjustment means. This can ensure that any adjustment of the adjustment means is transferred substantially completely to the printhead.
The apparatus preferably comprises means, mountable on the base, for shielding the adjustment means in order to prevent accidental adjustment of the position of the or each printhead on the base.
The apparatus may further comprise a slotted member, mountable on the base, having at least one slot formed therein so that fluid ejected from the or each printhead passes through a respective slot.
Each printhead may comprise a plurality of nozzles formed in a nozzle plate, the nozzle plate and the walls of the slot through which ink ejected from the nozzles passes defining at least part of a recess into which ink removal means is movable to remove any ink collected in the recess following ejection from one of the nozzles.
The present invention also provides apparatus for positioning an object relative to a datum, said apparatus comprising a base bearing said datum and comprising means for receiving an object, a plurality of tapered adjustment members each being movable relative to the base, and means for urging a received object against the adjustment members so that movement of an adjustment member relative to the base adjusts the position of a received object relative to said datum.
Preferably, said adjustment members comprise a first adjustment member for adjusting the location of a received object relative to the datum and a second adjustment member for adjusting the orientation of a received object relative to the datum.
Preferably each adjustment member comprises a tapered screw engaging a conformingly tapered bore formed in the base.
Preferably, the urging means is resiliently mounted on the base.
The receiving means may comprise a frame for receiving an object, the position of the frame relative to the datum being adjustable by moving said adjustment members.
The present invention further provides apparatus for positioning a plurality of objects relative to a datum, said apparatus comprising a base bearing said datum and comprising a plurality of receiving means each for receiving a respective object, and, for each receiving means, a plurality of tapered adjustment members each being movable relative to the base and means for urging a received object against the adjustment members so that movement of an adjustment member relative to the base adjusts the position of a received object relative to said datum.
The apparatus is preferably for positioning one or a plurality of printheads such that a swath of print produced by the or each printhead is in a predetermined position relative to the datum, the base being locatable on a printer using the datum.
The present invention yet further provides a method of positioning an object relative to a datum borne by a base comprising means for receiving an object, a plurality of tapered adjustment members each being movable relative to the base, and means for urging a received object against the adjustment members, the method comprising the steps of mounting an object in said receiving means and moving an adjustment member relative to the base to adjust the position of the received object relative to said datum.
The method preferably comprises the steps of moving a first adjustment member to adjust the location of the received object relative to the datum and moving a second adjustment member to adjust the orientation of the received object relative to the datum.
Non-ejection of droplets from droplet ejection apparatus, such as drop-on-demand ink jet printing apparatus, can result from the presence of air bubbles in droplet fluid housed in a fluid chamber communicating with the nozzle. Air bubbles can interfere with the acoustics within a fluid chamber to such a degree so at to prevent droplet ejection from the chamber. Due to the small size of the nozzles, it is difficult to remove air bubbles from the chamber without effectively xe2x80x9cflushing outxe2x80x9d the entire system.
In its preferred embodiments, the present invention seeks to solve these and other problems.
The present invention provides a printhead comprising:
at least one fluid chamber having actuator means actuable by electrical signals to effect ejection of droplets therefrom; and
conduit means for conveying droplet fluid towards and/or away from the or each fluid chamber, and for leading air bubbles in said droplet fluid to an air outlet.
By leading air bubbles in the droplet fluid to an air outlet, such as an air bleed outlet, the presence of air bubbles in the fluid chambers can be avoided.
The printhead may comprise a fluid inlet for supplying fluid to said at least one fluid chamber, and a filter disposed between said at least one fluid chamber and said fluid inlet, said conduit means being arranged to convey droplet fluid from said fluid inlet to said filter. The conduit means may be serpentine.
Thus, the present invention also provides a printhead comprising at least one fluid chamber having actuator means actuable by electrical signals to effect ejection of droplets therefrom, a fluid inlet for supplying fluid to said at least one fluid chamber, a filter disposed between said at least one fluid chamber and said fluid inlet, and serpentine conduit means for conveying droplet fluid from said fluid inlet to said filter. The printhead preferably comprises an air outlet, said serpentine conduit means being arranged to lead air bubbles in fluid conveyed thereby to said air outlet.
The air outlet may be disposed between said serpentine conduit means and said filter. The air outlet may be adapted to convey fluid away from said filter, that is, the air outlet may also be a fluid outlet of the printhead.
The at least one fluid chamber may be formed in a sheet comprising a layer of piezoelectric material, with the conduit means being formed in a cover bonded to said sheet. The filter may be integral with the cover.
The present invention further provides a printhead comprising a sheet comprising a layer of piezoelectric material, at least one fluid chamber being formed in said sheet, a cover bonded to said sheet, and serpentine conduit means formed in said sheet for conveying droplet fluid to said at least one fluid chamber. Preferably, a filter is formed in said sheet so that fluid conveyed from said serpentine conduit means to said at least one fluid chamber passes through said filter.
In a piezoelectric drop-on-demand ink jet printhead, an acoustic pressure wave is generated by an electrical signal to eject a droplet of fluid (e.g. ink) from a fluid chamber. The apparatus may have a single such fluid chamber, but more typically has a printhead with an array of such chambers each with a respective nozzle, the printhead receiving data-carrying actuating electrical signals which provide the power necessary to eject droplets from the chambers on demand. Each chamber is bounded by a piezoelectric element which is caused to deflect by the actuating electrical signal, thereby generating the acoustic pressure wave which ejects the droplet. Reference is made to our published specifications EP 0277703, U.S. Pat. No. 4,887,100 and WO91/17051 for further details of typical constructions.
During printing, heat is generated in a fluid chamber by actuation of the piezoelectric element. Some of this heat is transferred to the ejection fluid in the chamber, which can give rise to a variation in the viscosity of the ejection fluid between the fluid chambers. Such variations in the viscosity of the ejection fluid can give rise to variations in droplet ejection velocity and consequent dot placement errors in the printed image.
In its preferred embodiments, the present invention also seeks to solve this and other problems.
The present invention provides in another aspect a printhead comprising a base, at least one fluid chamber formed in said base, means for ejecting fluid from said at least one fluid chamber, a cover attached to said base, and a heat sink attached to the cover for dissipating heat generated in the printhead during the ejection of fluid from said at least one fluid chamber.
By attaching a heat sink to the cover, heat generated in the printhead during the ejection of fluid from a fluid chamber can be quickly dissipated from the fluid chamber, thereby minimising the duration of any significant variation in the viscosity of fluid in the fluid chamber.
The use of a heat sink can also enable the temperature of fluid in ejecting and non-ejecting fluid chambers to be rapidly equalized by distributing heat generated during fluid ejection amongst the fluid chambers, thereby minimising any variation in the viscosity of the fluid between the chambers. Accordingly, the present invention also provides a printhead comprising a base, a plurality of fluid chambers formed in said base, means for ejecting fluid from said fluid chambers, a cover attached to said base, and a heat sink attached to the cover for distributing amongst said fluid chambers heat generated during the ejection of fluid from said printhead.
To improve heat transfer from the fluid to the heat sink, the cover is preferably formed from material having a higher thermal conductivity than said base. Preferably, the cover is formed from material having substantially the same coefficient of thermal expansion as the base, so as to avoid distortion of the printhead that might otherwise occur as a result of the differing thermal expansion characteristics of the material of the base and the material of the cover. For example, the cover may be formed from silicon or aluminium nitride, and the base may be formed from piezoelectric material.
Preferably, the cover comprises fluid supply means for supplying fluid to said at least one fluid chamber. The heat sink may comprise a fluid inlet for conveying fluid to said fluid supply means. Preferably, the heat sink comprises a plurality of fins disposed side by side in a row.
To enable heat to be rapidly dissipated from the heat sink, the printhead preferably comprises means for supplying a stream of coolant fluid, such as a pressurized air stream, to the printhead.
The printhead preferably comprises a casing for said printhead, said casing comprising an inlet for receiving said stream of coolant fluid and an outlet for said coolant fluid. This can enable the drive circuitry which supplies the actuating electrical signals also to be cooled by the coolant fluid, thus reducing the likelihood of overheating of the drive circuitry.
Preferably, means for adjusting the pressure of the coolant fluid within said casing are provided. Means for adjusting the rate at which said coolant fluid stream enters the casing are also preferably provided. Valves may be provided at the inlet and outlet of the casing to adjust both the air flow and air pressure within the printhead.
In one preferred embodiment, the cover comprises at least one substantially planar sheet.